A new report suggests that the changes to the rate of wastewater inject in disposal wells could be one of the factors that lead to a giant Oklahoma earthquake last year in Pawnee. The town was struck by a magnitude 5.8 quake that was felt across the whole state.
In a report published yesterday in the Seismological Research Letters titled "Rupture Process of the Mw 5.8 Pawnee, Oklahoma, Earthquake from Sentinel‐1 InSAR and Seismological Data," by Raphaël Grandin, Martin Vallée, Robin Lacassin, it was stated that the earthquake was the largest one recorded in the state since the 1950s. It was also reported that previous Oklahoma earthquakes since 2009 were thought to be triggered by the wastewater produced by drilling of oil and gas that was injected back into the ground.
The earthquake in Oklahoma that has occurred in the region with active wastewater disposal wells is potentially the largest induced earthquake to happened in Oklahoma so far. This was written by Xiaowei Chen and Norimitsu Nakata from the University of Oklahoma in their preface to the section.
In an article published in Phys.org, Andrew Barbour and his colleagues at the US Geological Survey examined the new injection data from nearby disposal wells in the Osage County. They found out a significant increase in injection rates in the years before the major Oklahoma earthquake. Some wells have injected wastewater in Pawnee, Oklahoma at a constant rate. Meanwhile, others injected water at a variable rate, causing the overall injected volume to be roughly the same between the two types of wells.
In the model of injection by Barbour and his colleagues, it indicates that it may have been the variable-rate wells that were important for the Pawnee, Oklahoma earthquake. Their findings also suggested that a "long-term injection may have been responsible for a gradual loading of the fault in where it primed the fault for failure triggered by this short-term high-rate injection. However, they noted that the absence of these variable rate injections may have caused the failure of the fault much later time.
